A fuel control meters fuel to a gas turbine engine. The fuel control, simplisticly speaking, includes a pressure regulating valve (PRV) and a metering valve. The PRV maintains a pressure drop of the fuel across the metering valve at a fixed constant. By maintaining the pressure drop across the metering valve, an accurate weight flow (W.sub.F) of fuel may be provided to the gas turbine engine. However, a fixed constant pressure drop may not be desireable for all altitudes. At higher altitudes engines generally require less fuel to maintain engine power so that a smaller constant pressure drop across the metering valve is required. Conversely, at lower altitudes engines require more fuel to maintain engine power so that a greater constant pressure drop across the metering valve is required.
U.S. Pat. No. 2,605,709 to Jubb entitled "FUEL METERING MEANS FOR GAS TURBINE ENGINE FUEL SYSTEMS" shows a valve that controls the output of a variable displacement fuel pump to control the volumetric supply of fuel to provide the proper amount of fuel to a gas turbine engine at given altitudes. Variable fuel pumps are complicated and may be unreliable.
Other types of pressure regulation are sought and it is to this end the present invention is directed.